In floor hot water heaters, it is presently customary to form the hot water carrying pipe coil of plastic. However, when forming the pipe coil of plastic, it has been found that not only is the heat transfer to the surrounding concrete and the uniform heat distribution to the entire floor surface relatively poor, but also satisfactory laying of the pipe coil presents difficulties. In known arrangements, the plastic pipe is formed into a pipe coil on the spot, by bending, and the pipe ducts and pipe bends are then secured, for example by means for clips or binding wire, on an insulating base or on a concrete lattice, forming a sub-floor, after which the concrete floor is poured. However, it is practically impossible to secure the parallel pipe ducts at exactly equal spacings from each other and with exactly the same connecting bends. The relatively rigid plastic pipes frequently used for this purpose also must be heated in order to enable them to be fixed in a somewhat correct position by means of the clips, which are laid according to a predetermined assembly plan.
Additionally, where parallel pipe ducts are interconnected by metal plates, acting in the manner of clips, to improve the heat transfer, an exactly parallel and constant spacing of the parallel ducts is particularly important.